The airline suffered a major IT outage on Saturday and canceled all its flights leaving from London’s Heathrow and Gatwick airports before 6 p.m. local time. Outside of London, British Airways passengers faced extreme delays and were stuck on the tarmac for hours.

“The terminals at Heathrow and Gatwick have become extremely congested and we have cancelled all flights from Heathrow and Gatwick before 6pm UK time today, so please do not come to the airports,” British Airways said in a statement to CNN.

We apologise for the current IT systems outage. We are working to resolve the problem as quickly as possible.